1. Field of the Invention
This invention relates to a semiconductor substrate, more particularly to a semiconductor substrate for growth of an epitaxial semiconductor device.
2. Description of the Related Art
In optoelectric devices, a substrate suitable for growth of epitaxial layers thereon usually has a preferable lattice mismatch with the epitaxial layers, but has disadvantages, such as poor heat conductivity. Conversely, a substrate having a relatively high heat conductivity usually has a problem of lattice mismatching, which results in production of a number of threading dislocations. An existing method of making a semiconductor substrate is generally carried out by removing the substrate (sapphire) from the epitaxial layers and by attaching a heat-dissipating layer having a high heat conductivity to the epitaxial layers so as to maintain quality of the epitaxial layers and so as to enhance heat conduction.
U.S. Patent Application Publication No. 2008/0038857A1 discloses a method of making a gallium nitride-based semiconductor light-emitting device. The method includes steps of forming a sacrificial layer interposed between a substrate and a semiconductor epitaxial structure, and wet etching the sacrificial layer so as to remove the substrate from the semiconductor epitaxial structure. However, such removal has a disadvantage of poor etching efficiency due to side etching.
U.S. Pat. No. 5,073,230 discloses a method of making a semiconductor device. The method includes forming a plurality of etching holes that extend through a sacrificial layer and directing an etchant through the etching holes to eliminate the sacrificial layer. Formation of the etching holes increases an etching area and an etching rate. However, since the sacrificial layer itself is a dense film structure, the etching efficiency is still poor.